Bottom Line:
Perception is often influenced by context.By correlating the noise with observers' classification decisions, we found that the sizes of the surrounding contextual elements had a direct influence on the relative weight observers assigned to regions within and surrounding the central element.Specifically, observers assigned relatively more weight to the surrounding region and less weight to the central region in the presence of smaller surrounding contextual elements.

ABSTRACTPerception is often influenced by context. A well-known class of perceptual context effects is perceptual contrast illusions, in which proximate stimulus regions interact to alter the perception of various stimulus attributes, such as perceived brightness, color and size. Although the phenomenal reality of contrast effects is well documented, in many cases the connection between these illusions and how information is processed by perceptual systems is not well understood. Here, we use noise as a tool to explore the information processing correlates of one such contrast effect: the Ebbinghaus-Titchener size-contrast illusion. In this illusion, the perceived size of a central dot is significantly altered by the sizes of a set of surrounding dots, such that the presence of larger surrounding dots tends to reduce the perceived size of the central dot (and vise versa). In our experiments, we first replicated previous results that have demonstrated the subjective reality of the Ebbinghaus-Titchener illusion. We then used visual noise in a detection task to probe the manner in which observers processed information when experiencing the illusion. By correlating the noise with observers' classification decisions, we found that the sizes of the surrounding contextual elements had a direct influence on the relative weight observers assigned to regions within and surrounding the central element. Specifically, observers assigned relatively more weight to the surrounding region and less weight to the central region in the presence of smaller surrounding contextual elements. These results offer new insights into the connection between the subjective experience of size-contrast illusions and their associated information processing correlates.

Figure 1: Ebbinghaus–Titchener figures used as stimuli in the experiments. The central dots of the figures are the same physical diameter.

Mentions:
One size-contrast illusion, the Ebbinghaus–Titchener illusion (Titchener, 1901), has been used most extensively in this research. Figure 1 shows the canonical form of the Ebbinghaus–Titchener illusion. When most observers view these figures, the central dot is judged to be significantly larger when encircled by smaller dots (left side of Figure 1) than when surrounded by larger dots (right side of Figure 1 ). The magnitude of this effect has been shown to depend upon many additional factors, including the distance between the central dot and the surrounding dots, the number and density of surrounding dots, the similarity between the central and surrounding dots, and even the age, sex, and culture of the observer (Massaro and Anderson, 1971; Coren and Girgus, 1978; Weintraub, 1979; Weintraub and Schneck, 1986; Choplin and Medin, 1999; Phillips et al., 2004; Roberts et al., 2005; de Fockert et al., 2007; Daneyko et al., 2011). Nevertheless, the subjective experience of the Ebbinghaus–Titchener illusion is quite reliable and robust for most observers under a wide range of conditions.

Figure 1: Ebbinghaus–Titchener figures used as stimuli in the experiments. The central dots of the figures are the same physical diameter.

Mentions:
One size-contrast illusion, the Ebbinghaus–Titchener illusion (Titchener, 1901), has been used most extensively in this research. Figure 1 shows the canonical form of the Ebbinghaus–Titchener illusion. When most observers view these figures, the central dot is judged to be significantly larger when encircled by smaller dots (left side of Figure 1) than when surrounded by larger dots (right side of Figure 1 ). The magnitude of this effect has been shown to depend upon many additional factors, including the distance between the central dot and the surrounding dots, the number and density of surrounding dots, the similarity between the central and surrounding dots, and even the age, sex, and culture of the observer (Massaro and Anderson, 1971; Coren and Girgus, 1978; Weintraub, 1979; Weintraub and Schneck, 1986; Choplin and Medin, 1999; Phillips et al., 2004; Roberts et al., 2005; de Fockert et al., 2007; Daneyko et al., 2011). Nevertheless, the subjective experience of the Ebbinghaus–Titchener illusion is quite reliable and robust for most observers under a wide range of conditions.

Bottom Line:
Perception is often influenced by context.By correlating the noise with observers' classification decisions, we found that the sizes of the surrounding contextual elements had a direct influence on the relative weight observers assigned to regions within and surrounding the central element.Specifically, observers assigned relatively more weight to the surrounding region and less weight to the central region in the presence of smaller surrounding contextual elements.

ABSTRACTPerception is often influenced by context. A well-known class of perceptual context effects is perceptual contrast illusions, in which proximate stimulus regions interact to alter the perception of various stimulus attributes, such as perceived brightness, color and size. Although the phenomenal reality of contrast effects is well documented, in many cases the connection between these illusions and how information is processed by perceptual systems is not well understood. Here, we use noise as a tool to explore the information processing correlates of one such contrast effect: the Ebbinghaus-Titchener size-contrast illusion. In this illusion, the perceived size of a central dot is significantly altered by the sizes of a set of surrounding dots, such that the presence of larger surrounding dots tends to reduce the perceived size of the central dot (and vise versa). In our experiments, we first replicated previous results that have demonstrated the subjective reality of the Ebbinghaus-Titchener illusion. We then used visual noise in a detection task to probe the manner in which observers processed information when experiencing the illusion. By correlating the noise with observers' classification decisions, we found that the sizes of the surrounding contextual elements had a direct influence on the relative weight observers assigned to regions within and surrounding the central element. Specifically, observers assigned relatively more weight to the surrounding region and less weight to the central region in the presence of smaller surrounding contextual elements. These results offer new insights into the connection between the subjective experience of size-contrast illusions and their associated information processing correlates.